Chromatography is a process for separating mixtures by virtue of their differences in absorbency. FIG. 1 illustrates one embodiment of a typical chromatographic system. Although there are other types of chromatography (e.g., paper and thin layer), most modern applications include a mobile phase and a stationary phase and the separation of the fluid mixture takes place in a column.
The column is usually a glass or metal tube of sufficient strength to withstand the pressures that may be applied across it. The control over column temperature is critical to the resolving efficiency of the column, whether the system is designed to operate isothermally or by temperature programmed analysis. Such column temperature control can be achieved by heating of the column in a convection oven (as shown) or by resistance heating techniques.
The column can be, for example, a packed bed or open tubular column. The column contains the stationary phase of the process, i.e., the material for which the components to be separated have varying affinities. The mobile phase of the chromatographic process is comprised of a solvent or mixture of solvents into which the sample to be analyzed is injected. The mobile phase enters the column and the sample is absorbed onto the stationary phase. The solvent or solvent mixture is not absorbed on the stationary phase, but passes through the column.
As illustrated in FIG. 1, a first pump is used to draw a first solvent from a tank and supply it at a desired flow velocity and pressure to a T-shaped piping connector. A second pump is used to draw a second solvent from a second tank and supply it at a desired flow velocity and pressure to the T-shaped piping connector. At the T-shaped piping connector, the solvents are blended to achieve a solvent mixture having desired properties. The flow velocity of each solvent can be adjusted over time so as to vary the composition of the solvent mixture over time. A variation in the solvent mixture over time is called a solvent or compositional gradient.
A third pump is used to supply the sample or feed to a second T-shaped piping connection where it is injected into the solvent mixture and blended therewith, forming the mobile phase.
The mobile phase runs through the column and the sample is absorbed onto the stationary phase. As the sample flows through the column, its different components will adsorb to the stationary phase to varying degrees. Those with strong attraction to the support move more slowly than those with weak attraction. This difference in speed of movement is how the components are separated.
After the sample is flushed or displaced from the stationary phase, the different components will elute from the column at different times. The components with the least affinity for the stationary phase will elute first, while those with the greatest affinity for the stationary phase will elute last. A detector analyses the emerging stream by measuring a property, which is related to concentration and characteristic of chemical composition. For example, the refractive index or ultra-violet absorbance is measured.
A disadvantage associated with the system disclosed in FIG. 1 is that temperature of the fluid mixture or mobile phase provided to the column and column heater is not always constant, especially in long (multi-hour) chromatographic runs where room temperature swings are non-trivial. These temperature gradients can adversely impact the accuracy of the chromatographic analysis.
In view of the above, there is a need for a device for use with a chromatographic system, which pre-heats the sample before it is injected into the column and provides a tighter level of column heater sensitivity by minimizing the column inlet fluid temperature fluctuations. Still further, there is a need for a device that passively (i.e., without requiring a separate heating element and control system) pre-heats the mobile phase prior to its entry into the column and reduces sample band spreading or dispersion.